How to set value in session across all the website

I am developing an multi language application completed my admin side how integrating front end with my application. issue is i have 2 flags Russian and English i set default language English which works fine but when i click on Russian flag

Code:

it takes 1 as a value i store it in session but it works for one page only how can i use this 1 value across whole website so the complete website can run in that specific language i don't know how to pass values across multiple controllers or web-pages